This invention relates generally to brake mechanisms for electric motors and the like and, more particularly, pertains to spring-set, electromagnetically released brake mechanisms having minimal brake drag, advanced noise and wear suppression and improved sealing capability.
The invention arose during continuing development efforts relating to motor assemblies having brake mechanisms such as shown in U.S. Pat. Nos. 5,186,287, 4,798,269, 4,181,201 and 4,042,077 and as shown in "Stearns Spring-Set Disc Brakes", Catalog No. 200, 68910M, Stearns Division, Rexnord Corporation, 1989 and Stearns Spring-Set Disc Brakes Parts List for 55,000 Series, Sheet 309, effective Oct. 31, 1985, page S-607-1, Stearns Division, Rexnord Corporation.
The brake mechanism selectively stops or permits rotation of a shaft journaled in the motor frame. One or more friction discs secured to the shaft rotate therewith about the axis of the shaft. An end plate is secured to the motor frame, and has one or more non-rotatable pressure plates mounted thereto for axial movement toward and away from the friction discs. A lever is mounted to the end plate for pivotal movement toward and away from the pressure plates. Compression springs bias the lever against the pressure plates such that the pressure plates engage the friction discs and prevent rotation of the motor shaft. A solenoid is secured to the support plate and has a reciprocally movable plunger connected to the lever and movable to a first position moving the lever one axial direction away from the pressure plates against the bias of the compression springs to release the friction discs and permit rotation of the shaft. The plunger is movable to a second position permitting the lever to move under the bias of the compression springs in the opposite axial direction toward and engaging the pressure plates such that the pressure plates engage the friction discs and prevent rotation of the shaft. This basic structure is common in the industry.
The present invention provides enhancements in cost reduction, ease of maintenance and improved performance and life.
In one aspect of the invention, slots formed in the end plate are utilized for accepting separator springs biasing the pressure plates away from the friction discs in the released condition of the brake to minimize brake drag otherwise caused by contact of the pressure plates and friction discs during rotation of the motor shaft. In vertically mounted orientations of the motor brake, the gravitational weight of the pressure plates themselves may cause brake drag against the friction discs during rotation of the motor shaft. It is known in the prior art to secure leaf springs to the end plate to minimize brake drag as shown in U.S. Pat. No. 4,798,269. It is also known in the prior art to provide low force compression springs around pins secured to the end plate for performing such function, as shown in "Stearns Spring-Set Disc Brakes Part List for 55,000 Series", PTC sheet 309, Oct. 31, 1985, page S-607-1, FIGS. H, I, J, K and L. In the later embodiment, the brake must be specially modified by drilling holes in the end plate and in outer protrusions of the pressure plates, and inserting pins into such holes, which pins receive the low force compression springs. It is further known in the prior art to use low force compression springs around a plurality of studs which non-rotatably mount the pressure plates to the end plates and are spaced circumferentially around the friction discs as shown in U.S. Pat. No. 5,186,287. Depending on the nature of the brake application, various size leaf springs and low force compression springs must be installed for proper brake operation. The separator springs of the present invention not only minimize brake drag, but also significantly muffle the rattling backlash caused by the pressure plates in the slots of the end plate. In addition, the separator springs effectively prevent portions of the pressure plate which are normally thrusted into the slots from rotational forces during braking from gouging into the slots, thereby reducing braking torque.
In another aspect of the invention, a housing having an open end is operatively connected to the end plate for enclosing the brake mechanism and the sealing arrangement surrounding the open end of the housing is utilized for sealing the juncture between the end plate and the housing. A hub secured to the shaft and mating with the friction discs is provided with a radial seal retained in the end plate on an end adjacent the motor frame. Housing fasteners are provided with sealing rings between the heads of the fasteners and the wall of the housing to complete a dust-tight, waterproof seal and retain the housing in position against the end plate.
In another aspect of the invention, friction discs are secured to the shaft for rotation above the axis of the shaft, an end plate is secured to the motor frame, and non-rotatable pressure plates are mounted to the end plate for axial movement toward and away from the friction discs. A support plate is connected to the end plate and a lever is mounted to the support plate for pivotal movement toward and away from the pressure plates. A biasing arrangement biases the lever against the pressure plates such that the pressure plates engage the friction discs and prevent rotation of the shaft. A solenoid device is secured to the support plate and has a reciprocally mounted plunger operatively connected to the lever and movable between a first position to release the friction discs and prevent rotation of the shaft, and a second position to engage friction discs to prevent rotation of the shaft. Separator springs enveloping certain peripheral portions of the pressure plates are utilized for urging the pressure plates away from the friction discs in the first position of the plunger to minimize brake drag caused by contact of the pressure plates and the friction discs during rotation of the shaft, and for suppressing noise and wear caused by contact of the certain peripheral portions of the pressure plates relative to the end plate during operation of the brake mechanism.
In another aspect of the invention, a switching arrangement is provided to indicate relative wear of the friction discs by monitoring the position of the solenoid plunger.